Integrating the stable isotope and nutritional ecology of an East African forest

1Department of Anthropology and The New York Consortium in Evolutionary Primatology (NYCEP), The Graduate Center, City University of New York, 2Department of Biology, University of Utah, 3Department of Geology and Geophysics, University of Utah, 4Department of Anthropology, Hunter College, City University of New York

Stable isotopes are commonly used to reconstruct the diets and habitats of living and fossil animals. We sampled plants from Kanyawara, Kibale National Park, Uganda to investigate the stable isotope ecology of an East African tropical forest which is home to 13 primate taxa. We measured stable carbon and nitrogen isotopes, as well as protein, fiber, total non-structural carbohydrates, and lipids in 266 samples of 36 species. Leaf carbon isotope values reflected the well-known canopy effect, an isotopic depletion in the forest subcanopy due to decreased light and photosynthetic use of soil respirated carbon dioxide. While leaves separated isotopically by canopy layer, this pattern was not evident within the crowns of individual trees. Stable nitrogen isotope values exhibited the opposite pattern, with midstory leaves exhibiting the most enriched values and canopy, emergent, and gap/edge leaves respectively more depleted. Intra-specific differences in carbon isotope values were detected between mature and young leaves among five tree species. A weak negative relationship was found between carbon isotope values and leaf cellulose content (r2 = 0.2559, p < 0.005), as well as between carbon isotope values and a fiber (hemicellulose+cellulose) to protein ratio (r2 = 0.3438, p < 0.0005), which may represent an index of leaf toughness. Isotopic variability is thus associated with the nutritional composition and structural characteristics of forest foliage, which are significant for primate leaf selection. While causal relationships are uncertain, these data highlight the need to consider multiple correlates of isotopic variability within tropical ecosystems.

This research was funded by the New York Consortium of Evolutionary Primatology (NYCEP), NSF DGE 0333415 (NYCEP IGERT), and NSF MRI 0922709.